"But would Israel use tactical nuclear weapons - if it had them - to do so?"
No they wouldn't. Because if they did that would open up Pakistan and India using them in Kashmir, South & North Korea using them. It would legitimatize the use of nukes as a preemptive measure, which means NK may get one off against the US and with a RAT congress in, we may not get to retaliate.
What Israel should do is threaten to launch a conventional attack on Irans oil terminals. The reason Iran is not getting touched is because they are hiding behind their oil. Threaten to destroy that and now see how quick China and Europe tell Iran to stop.
In a fight for your continued existance, you don't abstractly ponder the implications that using a tool to save your life might allegedly set a precidence for some criminal to abuse a similar tool against someone else.
"Detatched reflection is not required in the presenece of an upraised knife."